Experimental study on the effect of pre-oxidation regulation on coal devolatilization and NOx emission during char combustion in O2/CO2/H2O atmosphere under pressurized conditions

• Pre-oxidation suppressed NO x effect in pressurized oxy-fuel combustion was studied. • Analyzed the contribution of devolatilization and char combustion to NO x emissions. • Proposed a pre-oxidation optimization strategy for NO x reduction. Pressurized oxy-fuel combustion is a potential carbon capture technology in coal-fired power generation. Pre-oxidation is an effective means to reduce NO x emissions during coal combustion. In this study, a pressurized horizontal furnace experimental system was used to explore the effects of pre-oxidation temperature (750–1000 °C), O 2 concentration (0.5–10 %), gasifying agent and residence time (1–7 min) on the generation of CO, CO 2 , CH 4 and NO x in the devolatilization stage of pulverized coal and the generation of NO x when char was burned in an O 2 /CO 2 /H 2 O atmosphere at 1.3 MPa. The contribution of the devolatilization the char combustion stage to NO x generation was comprehensively analyzed, and a pre-oxidation strategy suitable for pressurized oxy-fuel combustion NO x reduction was proposed. The results showed that pre-oxidation of pulverized coal at low oxygen concentration in the devolatilization stage can promote the generation of reductive CO and inhibit the generation of NO x . The NO x generation was the lowest at 2 % O 2 concentration at 1.3 MPa pressure and 800 °C. In the combustion stage of the char obtained by pre-oxidation, the modified char obtained by 2 % O 2 concentration has the least NO x generation. The NO x emission level in the whole combustion process can be controlled by increasing the reaction temperature in the pre-oxidation stage, extending the residence time as much as possible within the devolatilization degree of 80 %, and reasonably regulating the O 2 in a low concentration range to increase the devolatilization degree in the pre-oxidation stage. This work provided evidence that targeted pre-oxidation under pressurized conditions synergistically suppresses NO x formation across both devolatilization and char combustion stages, advancing the design of low-NO x pressurized oxy-fuel systems.